arm64: dts: imx8mp-phyboard-pollux: Add SD-Card vqmmc supply

Add SD-Card property for the bus IO power from the PMIC.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Reviewed-by: Yannic Moog <y.moog@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>